The invention relates to a system for controlling and/or regulating an electric machine of a motor vehicle, particularly a system for controlling and/or regulating a machine, such as a crankshaft starter generator, which can be operated as a generator and, as required, additionally as a motor.
A new generation of generators is known, which permit an access to the generator by way of a desired voltage predefinition, as well as additionally by way of an exciting current limitation. As a result of the generator construction, either the desired voltage predefinition or the exciting current predefinition has priority here. This means that, in the event of isochronous demands at the input of the desired voltage predefinition and at the input of the exciting current predefinition, in each case, only one demand (here: the exciting current predefinition) is taken into account. For example, in the case of contrasting demands on the generator and a prioritized exciting current predefinition, this may lead to a conflict of goals. That is, in the case of an active exciting current predefinition, by which, for example, the exciting current can be limited and thus the reciprocal action of the generator on the internal-combustion engine is controlled (limited), an electric power demanded by the desired voltage predefinition cannot be made fully available (see FIG. 1).
Furthermore, from German Patent document DE 103 01 531 A1, a system and a method for operating an electric machine are known, whereby the disadvantageous influences upon the drive transmission line that may possibly occur as a result of the operation of the electric machine, and the possibly occurring negative influences on the onboard power supply of a motor vehicle are to be avoided. For this purpose, it is suggested that a torque command variable be formed for the torque demands of the drive transmission line and that a voltage command variable be formed for the voltage demands of the onboard power supply and the battery. The voltage command variable is limited by upper and lower torque limiting values. The torque command variable is limited by upper and lower voltage limiting values.
It is an object of the invention to provide a system for controlling and/or regulating an electric machine of a motor vehicle, which ensures an improved coordination of demands on the electric machine.
According to the invention, this object is achieved as a result of the coordination of demands on the electric machine by way of prioritization devices and the assurance of a higher-ranking treatment of the demand with the highest priority by way of coordination devices. An unambiguous precedence of the possible demands on the electric machine is defined and thus also a sequence in the event of simultaneously occurring demands which would represent a conflict of goals. An uncontrolled or even accidental meeting of demands with correspondingly unpredictable consequences is reliably avoided.
In a preferred embodiment of the invention, the prioritization devices are constructed as a stored table, in which preferably all demands on the electric machine contemplated in the system are stored with an assigned individual priority. As an alternative, it is also possible to determine the priority for each occurring demand online according to previously determined rules and to assign it to the demand. For this purpose, software devices are available, for example, by way of which a priority is assigned to each demand, particularly as a function of influence factors whose change has at least an indirect influence on the torque of the electric machine. In particular, prioritization takes place as a function of the charge condition of the battery and/or as a function of the currently existing torque differential of the electric machine (torque differential=maximal torque−currently set torque).
Advantageously, precisely one priority is assigned to each demand, each priority to be assigned also existing only once in the system. Therefore, no conflicts can occur as a function of equal-priority demands.
Additional advantageous embodiments are described and claimed herein.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.